How can anybody say that this isn't a Christian nation?

Our legal system is based in the Judeo-Christian tradition (which also forms a good part of the Islamic legal system).  Despite the desperate attempts to deny this, and despite Supreme Court orders to remove plaques containing the Ten Commandments from schools and lesser courts, Levitical law is the basis of Western law. 

The base of this is in the Ten Commandments:

1. I am the Lord, your God.  You shall not have any other god before Me.
2. You shall not make any idols.
3. You shall not take the name of the Lord in vain.
4. Remember the Sabbath day, and keep it holy.
5. Honor your father and your mother.
6. You shall not commit murder.
7. You shall not commit adultery.
8. You shall not steal.
9. You shall not bear false witness.
10. You shall not covet.

The first five laws form the basis of our very culture.  The last five form the basis of our laws and legal system. 

The first three laws were set up to create a culture that honored and revered a God that the Israelites were, perhaps, less familiar with than they were with the gods of the land of their captivity.  The third one, however, just points out that God shouldn't be brought in as justification for atrocities (and yes, defensive war or not, the Crusades certainly carried their share of atrocities carried out under the banner of being "God's will"). 

The fourth commandment, the one about honoring the Sabbath, was as much about physical and spiritual rest and renewal as it was about God setting up the culture to worship and revere Him.

The next law, the one about honoring your parents, I suspect was as much because, at the time, parents were the most common method of cultural transmission. 

Much like today, honestly, only it's less the children dishonoring parents and parental rights, and more the government.

Laws 5-10 are what forms the base of the pedestal our laws rest on.  Don't kill each other.  Don't fuck each other's spouses (leads to murder and inbreeding).  Don't take each other's stuff.  Don't lie about each other (libel and slander).  Don't start wanting the goodies someone else has (leads to murder and theft--or to wanting to destroy someone else's property because they have it and you don't). 

So, how do we, as a nation, stack up under this?

Not so well, honestly.  How many people do you personally know that don't see anything wrong with loving something, anything, more than they do a God they can't be sure exists?  How many people practically worship celebrities?  How many of you have heard of the Westboro Baptists, who claim that God hates us all?  How about how often people choose to use their weekends working instead of resting from their work, as commanded? 

How about the government stomping all over parental rights and responsibilities?  Does anyone know how easy it is to get their kids yanked from their home and care?  Does anyone know what the schools are teaching, or how much of it goes directly against what we are trying to teach our kids?

As for the rest...look at the inner city thug culture.  The whole culture is based around murder, theft, sex, lies, and destruction of property because someone else doesn't have it and wants it. 

Does that mean that we aren't a Christian nation?  Not hardly.  All it means is that there's room for improvement.  We have done better in our history, and we can do better today.  We have the majority. 

We just need to stop turning the other cheek to those who would destroy us.  When Christ told us to turn the other cheek, that was only for personal insults, not attacks on our very existence.